How and when to harvest vermicompost and compost tea

After several months of loyal service, your worm composter rewards you with two distinct fertilizers: vermicompost, the dark brown material produced by your worms, and compost tea, a liquid fertilizer collected separately. Here's how to recognize the right time to harvest each one, and how to do it without losing your worms along the way.

When should you harvest?

The signal is unmistakable: when you have no empty tray left to add and your active tray, the one on top, is three-quarters full, it's time to harvest. For a first complete cycle, allow 3 to 6 months on average while your worm population settles in. Once you've hit your stride, harvests come around more regularly, roughly every 1 to 2 months, depending on how many food scraps you add and how much maintenance you're willing to put in.

It's also a good time to check that you have the right number of trays for your household: if the food scraps in the tray you're harvesting haven't all been fully broken down, it's a sign that you're one tray short. We cover this in more detail in our guide The stacking tray worm composter

Harvesting vermicompost, step by step

The tray to harvest is always the same one: the one at the very bottom, the oldest in the stack. It should be full of vermicompost, even if a few worms are still moving around in it.

Work by rotation: take out this bottom tray and place it at the very top of the stack, without putting the lid back on, under a light source. Because they're sensitive to light, your worms will naturally head down to take refuge in the darker trays just below.

Willy's tip

Scrape off the vermicompost in thin layers of 0.4–0.8 in (1–2 cm) and empty them into a bucket or container. Wait 5 minutes for the remaining worms to keep moving down, then repeat until the tray is empty.

Once the tray is empty, rinse it with water before putting it back on your worm composter. Take the opportunity to empty and clean your leachate tray: if your model has no filter between the leachate tray and the first tray, you'll often find a little precious vermicompost in it, carried down by worms that make their way to the bottom.

What if you don't have a stacking tray worm composter?

With a single bin, the rotation approach doesn't work quite the same way. Two methods work well: lay fresh bedding on just one side of the bin and put your next food scraps there, so the worms migrate on their own toward this new food source within a few weeks; or spread the contents of the bin into several small piles under a bright light, then scrape each pile in thin layers, letting the worms gather in the center, away from the light. If you use a continuous flow worm composter, harvesting works differently, from the bottom: we cover this in more detail in our guide The continuous flow worm composter

Harvesting compost tea

Compost tea — also known as worm tea, leachate, or compost juice — forms when your fruit and vegetable scraps release the water they contain: this liquid trickles down through the trays, picking up vermicompost on the way, and ends up in your leachate tray. Allow about 2 to 3 months before you get your first compost tea. You can then collect it through the spigot or drain hose, depending on your model. If yours doesn't have a spout, our Leachate collector makes harvesting easier.

Keep in mind that the less compost tea you produce, the better: it's a sign that you're adding enough carbon-rich materials, which absorb excess moisture — we cover these additions in more detail in our guide What do earthworms eat?

Willy's tip

Leave your spigot open at all times, with a container placed underneath. This prevents excess moisture from building up in your worm composter, and keeps any worms that have fallen in by accident from drowning.

Making the most of your vermicompost and compost tea

Vermicompost

Vermicompost is about 10 times more potent than regular compost — as we mentioned in our guide Worm composter or traditional composter: which should you choose? That's why it should be used in small amounts: allow 30% vermicompost to 70% potting soil. Rich in humus and microorganisms, it promotes germination, fertilization, and growth in your plants, flowers, vegetables, and fruit. Stored properly, it keeps for up to 2 years.

Willy's tip

Sift a 0.4–0.8 in (1–2 cm) layer of vermicompost over the top of your flowerpots: the fertilizer will reach the roots every time you water, for several weeks.

Compost tea

Compost tea is used diluted: allow 1 part compost tea to 9 parts water in your watering can, then water your plants as usual. Keep it for no more than 3 months, in a bottle that isn't tightly sealed — the active bacteria it contains need oxygen to stay effective. Before use, remember to shake the bottle (with the cap on this time) to re-oxygenate it.

Take the opportunity to maintain your worm composter

Harvest time is also the best time to clean your worm composter and extend its life: rinse your trays and leachate tray with water before putting them back into use. If possible, save the water you used for cleaning — it makes an excellent drink for your plants.

In summary

The signal is simple: no empty tray left and the active tray three-quarters full means it's time to harvest. A tray rotation and a few scraped layers of vermicompost are all it takes to separate your worms from their harvest, while the compost tea drips out separately through the spigot. Used in the right amounts — 30% for vermicompost, diluted to 10% for compost tea — each of these two fertilizers will feed your plants without ever burning them.

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